Telephone system



H. D. MACPHERSON- TELEPHONE SYSTEM.

APPLbCATION' FILED JULY 20. 1920. 1,386,719. Patented Aug. 9, 1921;

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H. D. MACPHERSON- TELEPHONE SYSTEM.

APPLICATION FILED JULY 20. I920.

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v ffugh D MacPherson.

H. D. MACPHERSON.

TELEPHONE SYSTEM.

APPLICATION FILED JULY 20, 1920.

3 SHEETS-SHEET 3.

/n verl for Hugh D. Mac Pheraon.

y W/Wy UNITED STATEE .PATENT (ilFElCE.

HUGH D. mcrnnnson, or- SUMMIT, NEW JnnsnY, Assic non To wnsrnnn nnnc d COMPANY, INCORPORATED, on NEW YQRK, n. r, A conrona'rio v or new YORK.

TELEPHONE SYSTEIqI.

Specification of Letters liatent.

Patented A11 9, 1921.

Application filed J'uIy 2D, 1920. Serial No. 397,641.

rated stations are controlled over a single.

signaling path common to such trunk lines.

in systems of this character heretofore employed there have been provided, at opposite ends of the signaling path, intermittently operated distributors, of the startstop type generally. employed in printing telegraph systems, for individually associating the trunk lines with the common signaling path, and for transmitting and receiving thereover code signals individual to the various trunk lines. For determining the code of the signals transmitted there have been provided intermittently operating selector switches comprising stationary contacts individual to the trunk lines and cooperating movable contacts individual to both those segments of the sending distributor which control the selection of the trunk lines at the receiving end, and those segments which control the character of the signal to be transmitted over the signal receiving Gonductor individual to the selected trunk line.

The principal object of this invention is the provision of improved means for determining the code of the signals to be trans mittod over .the common signaling path. Other objects will be apparent from a con-- sideration of the following description and the appended claims.

In the present emhodiment of the invention, there is provided at each end of the signaling path, a sending distributer and a receiving distributor common to the trunk lines: for transmitting and receiving code signals individual to the various trunk lines.

. -For determining the character of a-portion ments of the sending distributor which control the selection the trunk line at the receiving end. For determining the character of that portion of each code signal which controls the character of the signal to be transmitted over the signal receiving con-- ductor of the selected trunk line, there is provided means common to the trunk lines but independent oi the selector switch. This means preferably takes the form of a relay to directly control the polarity of current connected to one of the segments oi the sending distributor.

For a more complete understanding of this invention, reference should be had to the accompanying drawings in which Figs 1, 2 and with Fig. 2 placed to the right of Fig. l and Fig. 3 below F 2 illustrate certain portions oi a telephone system embodying the invention. All apparatus shown in Fig. 1 is located at an oilice X; th apparatus to the left of the dotted line in Fig. 2 and that in Fig. 3 is located at an oflice Y, while that to the right of the dotted line in Fig. 2 is located at an oi'hce Z. For convenience where like apparatus is employed at offices X and Y, it is designated by the same reference character, that at oflice X without, and that at office Y with primes. In the drawings there is shown a toll trunk line L 18 comprising two talking conductors extending from a jack 66 at central oi'lice X to a plug 219 at central oflice Y. ilt central otiice X there is located a toll cord circuit F for ex tending connections from calling line, (not shown) to the trunk lines. The trunk line L 18 may be connected with a toll swit-. -hing trunk circuit M omen-ding trom the central oflice Y to a central otlice Z at which termi nates a called subscrihers telephone line N with which the toll twitching trunlt circuit may be connected. ll hile only one tell cord circuit, one tell trunk line, one toll switching trunk and one subscribefis telephone line are shown, it is to be understood that this is for the purpose of simplicity only and that many such circuits may he and usually are provided in actual service.

The signals for a plurality of toll trunk lines may be controlled over a signaling path common to the trunk lines, consisting of a conductor P, extending from o'fliceX to oiiic Y and provided with a grounded return as shown. In order that signals may be simultaneously transmitted in both directions over the conductor P, there is provided the usual duplex equipment comprising dif ferential polarized relays 7 and 7 at opposite ends of the conductor, and artificial balancing lines AL.

Within the dotted inclosure SE in Fig. 1, there is shown signal transmitting equipment located at office X, which is common to a plurality of trunk lines and comprises a sending distributer S, a selector switch G, and controlling relays therefor: As the transmitting equipment located at office Y is identical with that at office X, it has been represented diagrammatically by the dotted squar SE in Fig. 3. To the right of the dotted line in Fig. 3 there is shown signal receiving equipment RE located at office Y, comprising a receiving distributer R, looking relays 27 to 32, and pyramid selecting relays 33 to 47. Since the receiving equipment at office X is identical with that at office Y, it has been represented diagrammatically by the dotted square BE in Fig. 1. A description of the equipment SE and RE will, therefore, serve to describe the equipment SE and RE as well.

The sending distributer S and the receiving distributer R are of the start-stop type well known in the art of printing telegraphy and comprise a set of stationary rings, some of which are continuous and some segmented, brush arms 8, 16, brushes 9, 10 and 17, 18, carried by and insulated from the brush arms, and release magnets SRM and RRM respectively. The brush arms 8 and 16 of distributers S and R at office X are mounted on a continuously rotating shaft and separated therefrom by friction clutch mechanism (not shown) so that upon the energization of either release magnet SRM or RRM, the brush arm normally held against rotation by the armature of that magnet will make one revolution being stopped at the end of the revolution by engagement with the armature of the release magnet which has been retracted during the rotation of the brush arm. The brush arms 8 and 16' of the distributers S and R at office Y are likewise mounted on a continuously rotating common shaft and operate in the same manner. Any well-known means, (not shown) may be employed to maintain syn chronism between the rotating shaft at office X and that at office Y. The face of sending distributer S is provided with a common sending ring 11 which is successively connected during a rotation of the brush 10 to a restoring segment 0, a start segment 8 and individual sending segments 1 to 6 for controlling the signals transmitted over the conductor P. A ring 12 which is successively connected during a rotation of the brush 9 with segments 13, 1st and 15 is also provided to control local circuits at office X. of receiving distributer R comprises seg- The face ments 24:. and 26 which control the circuit of release magnet RRM, a common receiving segment 19 which is successively connected by brush 18 to individual receiving segments 1 t0 6 to control relay 2? to 32 in accordance with the signals received over the conductor P, and segments 23 and 25 which complete the selected signaling cir cuit at office Y.. A ring 20 is also provided to cooperate with a segment 22 in controlling the circuit of relay The common signaling conductor P is connected through one winding of polarized relay 7 to the common sending ring 11 of distributer S at office X. Negative battery is normally connected through segment 1 to the conductor P, causing polarized relay 7 at office Y to maintain closed its lower contact. Upon the energization of release magnet SRM, the brush arm 8 starts its rotation in a clockwise direction and positive J battery is immediately connected through start segment 8 of distributer S to conductor P to cause relay 7' to close its upper contact, thereby completing a circuit for release magnet RRM of receiving distributer R at office Y. The energization of release magnet RRM releases brush arm 16 so that arm 8 at office X and arm 16 at office Y rotate in approximate synchronism. When negative battery is connected through any of the sending segments 1 to 6, through ring 11 to conductor P, it will cause the closure of the lower contact of duplex relay 7 at office Y, thereby completing a circuit from grounded battery, lowercontact of relay 7, receiving segment 19, one of the individual segments 1 to 6 in accordance with the position of the brush arms 8 and 16, through the lower winding of one of the relays 27 to 32 corresponding to the segments 1 to 6 to ground. When, however, positive battery is connected through one of the sending segments 1 to 6 and ring 11 to conductor P during the travel of brush arms 8 and 16, relay 7 maintains closed its upper contact and no effects are produced on the locking relays 27 to 32. It will, therefore, be apparent that by varying the code of the signals transmitted over the conductor P, any desired combination of the locking relays 27' to 32 may be energized. Each of the first four of these relays 27 to 30 controls the circuit for one row of the pyramid selecting relays 33 to 47, while the fifth locking relay 31. selects either the upper or lower armature of relay 33 so that the selection of the signal receiving conductor E to be associated with the distributer R de- The character of signal to dition of relay 3 2, the sixth of the locking relays, for if this relay is deenergized at the time brush 18 passesover segments 23, 25 negative battery will be connected over the lower armature and back contact of relay 32, segments 23, 25, lower armature of relay 31 and thence over the armatures oi other of the pyramid selecting relays to the conductor E which conductor is individual to the selected trunk line. If, however, rclay 32 is energized at this time, positive battery will be connected over the front con tact and lower armature of relay 32 and over the path just traced to conductor E.

The code of that portion of each signal 7 which controls the selecting oi? the conductor E individual to a given trunk line is, therefore, determined by the polarity of current connected to segments 1 to 5 of distributer S while the distributer is sending out a signal.

A selector switch G determines, by the position of its brushes 1 to 5, the polarity of current connected at any time to segments 1 to 5 of distributer S. The switch G comprises seven movable contacts or brushes a, Z), 1, 2, 3, 1 and 5 which are preferably mounted at different levels on a common shaft. Each brush cooperates with a set of stationary contacts, as shown, there being one stationary contact in each set for each trunk line which may be associated with the distributer S. The brushes of switch G may be rotated over their contacts either by a continuously driven source of power or by stepping magnet. In the present embodi ment of the invention a self-interrupting motor magnet MM is provided to move the brushes step-by-step over their contacts. The switch G will be started whenever relay l8, which is common to the trunk lines, is enei led, and will he stopped by the energiza n of relay 50 when the brush a, en ceunters a stationary contact connected over one oi the conducters A to ground, There is provided for each trunk line, one conductor A, leading from a stationary contact of the switch G to a back contact of the relay 61 which is individual to said line. Relay 48 is controlled over conductor C, common to the trunk lines, by certain relays individual to each trunk line. There is also provided for-each trunk line, a conductor B leading ttrom'the winding of individual relay 60 to that stationary contact upon whlch the brush Z) rests when the switch G has been associated with the particular trunk line in signaling condition. The stationary contacts of levels 1 to 5 of the switch G are connected to sources of current of positive and negative polarity in various combinations such as to cause the selection of the proper conductor E at oliice Y whenever one of the trunk lines at oi'hce X is in signaling condi tion. While the invention is not limited to any perific combination of polarities, nor to any particular number of trung lines which may be served by one selector switch and set of distributers, the combination shown in the following table have'been found satisfactory for use with a switch G having thirty contacts in each level to be used with a distributer S employing five sending segments in selecting the proper signal receiving conductor E at the distant oflice.

The code of that portion of each signal transmitted by distributer S which controls the character of signal to be transmitted over the selected signal receiving conductor E is determined by the polarity of current connected to segment 6 of distributer S dur ing signaling. This polarity is controlled by a relay 71 common to the trunk lines, which normally connects positive current to segment 6 over its right-hand armature and back contact, but which when energized connects segment 6 to a source of current of negative polarity. Relay 71 is initially energized upon the energization of a relay 19 and is locked up under the control of a release re lay 52 which will be actuated near the end of a revolution of brush arm 8 after a signal has been transmitted. Relay 4-9 is controlled over a conductor D common to the trunk lines, and will be energized at such times as the relays individual to any trunk line determine, as will more fully appear hereinafter.

Having in mind the foregoing description of the apparatus of the system shown in the drawings, it is believed that the invention will be readily understood from a consideration of the following description of the operation of setting up and taking down a connection from cord circuit F to the called station N.

U omiect'ion of 00rd circuit F with trunk Zme L18.

The operator at 'ofiice X desiring to.

establish connection with the telephone line with which must be established through the oflice Y, communicates over an order wire circuit (not shown) with the operator at ofiice Y. The operator at ofl'ice Y noting that trunk line L 18 is idle, designates this trunk for the completion of the connection whereupon the operator at oflice X inserts plug of cord circuit F in jack 66 of trunk line L 18. A circuit is thereby completed from grounded battery through the winding of marginal relay 53, sleeve contacts of plug 65 and jack 66, and the winding of'relay 55 to ground. Relay 55 is energized in this circuit but relay 53 being marginal remains inert. Relay 55 in energizing completes a circuit from ground, its armature and front contact, back contact, and outer right-hand armature of relay 57, back contact and righthand armature of relay 59, through the winding of relay 58, and back contact and lefthand armature of relay 60 to grounded battery. An energizing circuit is also completedfrom grounded battery, lefthand armature and back contact of relay 62, through the winding of slow release relay 63, and front contact and armature of relay 55 to ground. Relay 58 is energized in this circuit and locked up through its front contact and. inner right-hand armature. In attracting its outer left-hand armature, relay 58 places a ground on conductor C thereby causing the energization of start relay 48. Upon attracting its outer right-hand armature, relay 58 causes the operation of relay 56 over a circuit from ground, outer right-hand armature and front contact of relay 58, through the winding of relay 56 to grounded battery. Relay 56 is thereupon locked up to ground at the innermost lefthand armature of .relay 59. Relay 48 in attracting its armature completes a circuit from grounded battery, back contact and armature of motor magnet MM through the winding of said magnet, back contact and outer left-hand armature of relay 50, and. front contact and armature of relay 48 to ground. Magnet MM interrupts this circuit at its armature thereby stepping the brushes of the selector switch G in a clockwise direction until the terminals individual to the trunk line L 18 are encountered. yVhen brush a reaches the stationary contact associated with conductor A 18, stop relay 50 is energized over a circuit which may be traced from grounded battery, lefthand winding of relay 50, brush a, conductor A 18, back contact and outer left-hand armature of relay 61, outermost left-hand armature and back contact of relay 59, front contact and inner left-hand armature of relay 58 to ground. Relay 50 in attracting its outer left-hand armature, interrupts the previously traced circuit for magnet MM thereby stopping the selector switch G. In

attracting its outer righthand armature, relay 50 completes a circuit for release magnet SR-M of distributer S which may be traced from ground, winding of magnet SR-M, outer right-hand armature and front contact of relay 50, segment 13, brush 9, and ring 12 to grounded battery. Relay 50 when energized, was locked up over a circuit extending from grounded battery, inner lefthand armature and front contact ofsaid relay, back contact and armature of relay 52, through the right-hand winding of relay 50 to ground. The energization of magnet SRM releases brush arm 8 which starts its rotation in a clockwise direction. Considering first the results produced at ofiice X by this operation, it will be seen that upon reaching segment 14, a circuit will be completed from grounded battery, ring 12, brush 9, segment 14, through the winding of relay 51-t0 ground. Relay 51 will be energized in this circuit and maintained energized until brush 9 passes over segment 14. Relay 51 in attracting its armature, completes a circuit from grounded battery, inner lefthand armature and front contact of relay 50, back contact and armature of relay 52, armature and front contact of relay 51, brush 1), conductor B 18, through'the winding of relay 60 to ground. Relay 60 is energized in this circuit and in attracting its left-hand armature, interrupts the circuit of relay 58, which relay in retracting its .armatures removes the ground connected to conductors C and A 18 and opens the original circuit for relay 56. Relay 60 also completes a circuit from grounded battery, lefthand armature and front contact of said relay, left-hand armature and front contact of relay 56, through the winding of relay 57 which i s made slow to release, and back con tact and innermost left-hand armature of relay 59 to ground. Slowrelease relay 57 is energized in this circuit and locked up under the control of relay 59. Relay' 57 in attracting its right-hand armatures, interrupts the original energizing circuit for relay 58 and prepares a circuit for relay 59.

When brush 9 of distributer leaves segment 14 relay 51 deenergizes and in retracting its armature causes the dee'nergization of relay 60. hen brush 9 of distributer S reaches segment 15, a circuit is completed from grounded battery, ring 12, brush 9, segment 15, through the winding of relay 52 to ground. Relay 52 in attracting its armature opens the previously traced looking circuit of relay 50 to deenergize this relay, the origlnal energlzing' circuit of which was interrupted by the retraction of the armatures of relay 58. Relay 50 in deenergizing opens the previously traced circuit for magnet SRM, which magnet retracts its armatureto arrest the travel of the brush relay 27.

arm at the completion of its revolution and in retracting its outer'letthand armature. relay 50 again places the motor magnet MM under the control, of common start relay as. Brush 9 in passing from seg ment opens the circuit of relay 52 and the relays common to the sending equip ment SE are now all inert.

Considering now the effects produced at otlice Y by the rotation of brush arm 8, when brush 1O reached segment 3, a circuit was completed from the positive pole of battery, segment 8, brush 10, sending ring 11, through the upper winding of duplex relay 7, conductor P, through the upper winding of duplex relay 7 to SE. In response to this circuit, relay 7 closed its upper contact, completing a circuit from grounded battery, upper contact of relay 7, segment 24-, brush 18, segment 26, through the winding of magnet RRM to ground. Magnet RRM in attracting its armature released brush arm 16 which started a revolution in a clockwise direction. Upon reaching individual sending segment 1 of distributor S, brush 10 completed a circuit from the negative pole of battery,

brush 1 of selector switch G, individual sending segment 1, brush 10, sending ring 11, through duplex relay 7, conductor P and relay 7 to ground thereby causing relay 7' to close its lower contact. At this time, brush 18 was in contact with receiving segment 1' of distributer R, and a circuit was rompleted from grounded battery, lower contact of relay 7", receiving segment 19, brush 18, segment 1 and through the lower winding of relay 27 to ground. Relay 27' is energized and locked-up over a circuit extending from grounded battery, upper winding of relay 27, front contact and upper armature of said relay and armature and front contact of relay 70 to ground. ldelay 70 was energized when brush 17 completed a circuit from grounded battery, ring 20. brush 1'7, segment 22, through the winding 0:" relay T0 to ground. Since the polarity of battery connected through brush 2 of switch G to individual sending segment 2 is positive, relay 7 will close its upper contact when brushes 10 and 18 are passing over segments 2 and 2 respectively, so that no circuit will be completed for relay 28. When these; brushes reach segment 3 and 3, however, negative battery is again connected over the path P to cause relay 7 to close its lower contact to complete an energizing circuit for relay 29 in the same manner as the circuit was completed for relay 29 is locked up over an obvious circuit in parallel with the locking circuit traced for relay 27'. Since sending segments a and 5 are connected to the positive pole of battery, no effect will be produced on relays 30 and 31, as the brushes or distributor S and R pass over segments a, e and 5, 5, and since relay 71 is inert when the brushes pass from segments 6 and 6, no effect will be produced on relay 32. Thus, as brush 18 leaves segments 6 and 19 of distributer B, only the first and third of the locking relays, namely 27 and 29 will be energized. Relay 27 in energizing, completes a circuit which may be traced from grounded battery, through the wind ngs in series, of pyramid relays 4:0 to 4L7 inclusive and the front contact and lower armature of relay 27 to ground. Relay 29 in energizing, completes a circuit from grounded battery, through the winding of pyramid relays at and in series, and the front contact and lower armature of relay 29 to ground. As brush 18 engages segments 23 and 25 a circuit will be completed from the negative pole of battery, back contact and lower armature of relay 32, segment 23, brush 18, segment 25, lower armature and back contact of relay 31, lower armature and back contact of re lay 33, lower armature and front contact of relay 35, upper armature and back contact of relay 39', upper armature and front contact of relay 46, conductor E 18, through the lefthand winding of relay 200 to'ground. Relay 200 is energized in this circuit and in attracting its inner armature completes an obvious locking circuit for itself. Relay 201 was also energized in parallel with relay 200 but as no locking circuit was completed for relay 201, it wasimme-diately denergized and performed no useful func ion. Brush 1'? 0t distributer R in passing from segment 22 interrupted the circuit 01"- relay 70 to de'e'nergize this relay. The retraction of the armature of relay 70 opened the looking circuit for such of the locking relays 27 to 32 as have been energized. The deenergization of these locking relays opens the circuit of suchpyramid relays as have been energized thereby restoring the receiving equipment RE to its normal condition of readlness to receive the next signal transmitted over the conductor P.

Relay 200 in attracting its inner armature completed a circuit from grounded battery,

inner armature and front contact of relay 200, conductor 23!, back contact and lower armature of relay 216, through the guard that the operator at ofiice X has connected her cord circuit F to the designated toll line L 18.

Connection of toll Zine L 18 with toll switch ing trunk circuit M.

After the operator at ofiice Y designated the trunk line L 18 for use she communicated with the operator at ofiice Z over an order wire (not shown) advising the operator at office Z the number of the called line. The

operator at ofiice Z noting the idle condition of toll switching trunk M assigns it for use by the operator at office Y. The operator at oilice Y, noting the lighting of guard lamp 218, inserts plug 219 into jack 220 of toll switching trunk M thereby completing a circuit from grounded. battery, through the winding of sleeve relay 215, and sleeve contacts of plug 219 and jack 220 to ground. Relay 215 is energized in this circuit thereby completing an obvious circuit for relay 216. Relay 216 in attracting its lower armature opens the circuit previously traced for guard lamp 218 to extinguish such lamp. In attracting its upper armature, relay 216 completes a circuit which may be traced from grounded battery, through the lefthand winding of the supervisory relay 221 of trunk circuit M, back contact of relayits armature, completes a circuit extending.

from grounded battery through lamp 228, the lower normal contact of relay 227, the right-hand winding of relay 222 and the alternate contact of relay 221 to ground.

I Lamp 228 is lighted to inform the operator at oiiice Z that'the operator at oflice Y has made connection with trunk circuit M. Relay 222, in attracting its armatures opens the previously traced circuit for relays 221 and 223 so that although relay 223 may operate momentarily, it immediately releases and produces no material effect. The attraction of the left-hand armature of relay 222 completes a holding circuit to maintain relay 221 operated.

Connection of toll switching trunk circuit M with telephone line N.

The operator at oflice Z after testing the called line in the usual manner inserts plug 224 into jack 225. A circuit is thereupon completed from grounded battery, through the winding of sleeve relay 227, the sleeve contacts of plug 224 and jack 225 and the winding of cut-0E relay 226 to ground. Helays 226 and 227 operate the former disconnecting the line relay from the line in the usual manner and the latter completing the continuity of the tip conductor of the trunk and interruping the circuit for lamp 228 and relay 222. Lamp 228 is extinguished and the retraction of the armatures of relay 222 reestablishes the original energizing circuit for relay 221. However, due to open condition of the lower normal contact of relay 227, relay 222 does not reoperate although relay 221 remains operated. Relay 223 operates and in attracting its arniatures completes a circuit in parallel for relays 212, 213 and 21 that for relay 21% being traceable from grounded battery through the winding of relay 214i and front Contact and armature of relay 223 to ground. Relay 21&,is slow to release and relay 213, while somewhat slow in releasing, is faster in operating than relay 214. and relay 212 is a fast relay. The circuit for relay 213 may be traced from grounded battery, winding and make-before-breal; contact of said relay right-hand armature and back contact of relay 208, outer right-hand armature and back contact of relay 20a, conductor 238, front contact and armature of relay 223 to ground. Upon operating, relay 213 is locked up over a circuitfrom grounded battery, winding, front contact and righthand armature of said relay, inner left-hand armature and back contact of relay 206, back contact and outer right-hand armature of relay 20d, and'conductor 238 to ground at the front contact of relay 223. Relay 213 being somewhat slower in operating, did not attract its left-hand armature until after a circuit had been completed from grounded battery, through the winding relay 48' of sending equipment SE, conductor O, (back contact and outer left-hand armature of relay 208) through the winding of relay 212, left-hand armature and back contact of relay 213, and thence in parallel with the circuit traced. for relay 213 to ground at the front contact of supervisory relay 223. Re lay 212 in attracting its inner right-hand armature completed a locking circuit for relays 18and 212 independent of relay 213. Relay 48 in energizing, caused the selector switch G to seek with its brush, a grounded conductor A in the same manner as above described forthe sending equipment SE at office X. Relay 212 in attracting its outer left-hand armature, grounded conductor A 18 to stop selector switch G in association with the terminals individual to trunk line L 18. From this point the operation of sending equipment SE is identical withv that described for the sending equipment SE and results in the transmission of an impulse of negative current over the conductor E 18 through the right-hand winding of relay 62 to ground at ofiice X. Relay 62 in attracting its left-hand armature completes a locking circuit for itself from grounded battery, left-hand winding of relay 62 and front contact and armature of relay 55 to ground. In attracting its right-hand ar mature, relay 62 completes a circuit from ground, back contact and right-hand arma ture of relay 64, right-hand armature and front contact of relay 62, through the resistance 69, sleeve contacts of jack 66 and plug 65, through the winding of marginal relay 53 to grounded battery. The increased flow of current caused by the closure of this circuit a portion of which shunts the winding of relay 55 allows marginal relay 53 to'attract its armature but does not affect the energized condition of relay 55. Relay 53 in energizing, completes an obvious circuit for lamp 68 to inform the operator at oflice X that the connection has now been set up to the terminals of the desired line and that the established circuit is in condition for signaling the subscriber at the wanted substation.

Upon the operation of relay 51 of sending equipment SE, a circuit was completed from grounded battery, front contact of relay 51, brush Z2, and conductor B" 18 through the winding of relay 208 to ground to energize this relay in the same manner that the energization of relay'60 was brought about durin the transmission of a signal from office i to oilice Y. Relay 208 in attracting its outer left-hand armature, interrupted the locking circuit of relays 18 and 212 to deenergize these relays. At the time relay 212 was originally energized, a circuit was completed from grounded battery, inner armature and front contact of relay 200 through the winding of relay 205, back contact and left-hand armature of relay 209, front contact and inner lefthand armature of relay 212 to ground to energize relay 205. Relay 205 in energizing completed a circuit in parallel with that just traced through the armature and front contact of relay 205, the winding of relay 209 over the back contact and inner right-hand armature of relay 204; to ground, but relay 209 was not energized at this time since this circuit was shunted by the connection of ground from the inner left-hand armature of relay 212 to the armature of relay 205. Upon the deenergizing of relay 212, however, and the removal of this shunt ciruit, relay 209 is energized but is without effect at this time. The condition of the relays associated with the trunk line L 18 and office Y, after the sending of the ringing signal to oflice X, will therefore be as follows relays 200, 202, 205, 209, 213, 214i, 215, 216 and 223 energized and all other relays inert.

Operator at 077506 21 actuates ringing key.

The operator at office X upon observing the lighted condition of supervisory lamp 68, depresses her ringlng key 67 to complete -a circuit from a source of alternating current, loweralternate contact of key 67, ring contact-s of plug 65 and jack 66, through the winding of alternating current relay 5 1, tip contacts of jack 66 and plug 65, and upper alternate contact of key 67 to ground. Relay 54: is energized in this circuit and completes an obvious circuit for slow release relay 61. Relay 61in attracting its righthand armature completes a. circuit fronr ground, armature and front contact of relay 55, front contact and right-hand armature of relay 61, through the winning of relay 58, back contact and left-hand armature of relay 60 to grounded battery. Relay 58 is energized in this circuit and applied ground to conductors G and A 18 in exactly the same manner as when relay 58 was energized upon the insertion of plug 65 into jack 66. Since, however, relay 61 has opened these conductors at its left-hand armature-s, no efiect is produced through the continued depression of the ringing key by the operator at ofiice X. Upon the release of this key by the operator at office X, relay 5a is deenergized to open the circuit of relay 61 which, in retracting its right-hand armature opens the original energizing circuit of relay 58. This relay, however, is locked up as before, being under the control of relay 60 and since conductors C and A 18 are now grounded, the same sequence of operations is produced in sending equipment SE as was previously described upon the insertion of plug 65 into jack 66 and results in the sending of a code signal over conductor P to select the signal receiving conductor E 18 at office Y andto transmit an impulse of negative polarity over this conductor through the righthand winding of relay 201 to ground. Relay 201, in energizing, completes a locking circuit for itself which may be traced from grounded battery, left-hand winding front contact and armature of relay 201, armature and front contact of slow release relay 202 to ground. After the transmission of he impulse of negative current over conductor E 18, sending equipment SE at oflice X and receiving equipment RE at Y, are re stored to normal condition in the manner previously described, and of the relays inthe other relays individual to this toll line will be inert.

Relay 201, which was energized and locked up in response to the ringing signal received from oflice X, in attracting its right-hand armature,-completed a circuit from grounded battery, inner armature and front contact of relay 200, right-hand armature and front contact of relay 201 through the winding of slow release relay 203 to ground, and opened the circuit of slow release relay 202 so that after a short interval, relay 202 is deen-ergized to open the locking circuit of relay v201 which thereupon retracts its arinatures.

relay 217 and slow release relay 211 which 1 may be traced from grounded battery, through the windings of said relays, front contact and armature of slow release relay 207 to ground. Relay 211 connects ground to conductor 238 to replace the ground connected thereto on the left-hand armature of relay 203 which is removed upon the deen-ergization of relay 203 which takes place after a short interval, due to the retraction of the right-hand armature of relay 201; Relay 217 in opening its back contacts, interrupts the circuits of relays 223 and 221, but relay 221 does not deenergize owing to the completion of a substitute circuit as will appear later. Relay 217 in closing its front contacts completes a circuit from a source of alternating current'234, front contact and lower armature of relay 217, ring contacts of plug 219 and jack 220, through ringing response relay 230, tip contacts of jack 220 and plug 219, front contact and upper armature of relay 216, upper armature and front contact of relay 217 to ground. Relay 230 is energized in this circuit to complete a circuit from ground, armature and front contact of relay 230, through the winding of relay 233 and the left-hand winding of relay 222 to grounded battery. Relay 222 in energizing completes a holding circuit for relay 221 which may be traced from grounded battery, left-hand winding of relay 221, front contact and outer armature of relay 222 to ground. Relay 233, in attracting its armatures, completes a circuit from a source of alternating current 232, front contact and upper armature of relay 233, ring contacts of plug 224 and ack 225, through the'ringer at the called substation N, tip contacts of jack 225 and plug 224, front contact and upper armature of relay 227, lower armature and front contact of relay 233 to ground, thereby causing the operation of the call bell at the called substation.

Until the called subscriber answers, the lamp 68 remains lighted before the operator at oflice X, and if after a reasonable interval this lamp'is not extinguished, she will. again actuate her key 67 to cause another ringing signal to be transmitted over the path to again actuate the relays at offices Y and Zto ring the call bell at substation N. In case the called subscriber does not answer within a reasonable time, in response to repeated actuations of key 67 the operator at oflice X will report this fact and abandon the call. Vhen, however, the subscriber at 'station N answers, a circuit is completed which may be traced from grounded battery,

through the winding of called line supervisory relay 231, back contact and upper armature of relay 233, ring contacts of plug 224 and jack 225, apparatus at substation N, tip contacts of jack 225 and plug 224, front contact and upper armature of relay 227, lower armature and back contact of relay 233 7 to ground. Relay 231 is energized in this circuit and completes a circuit from grounded battery, through the left-hand winding of.

relay 222, front contact and armature of relay 231, right-hand winding of relay front contact and armature of relay 221 to ground to hold relay 222' energized during such time as the subscriber at station N rea 7 tains his'receiver away from its switchhook. During the intervals between ringing, relay 223 was alternately energized upon the retraction of the armatures of relay 217 which caused the denergization of ringing re-;-..

sponse relay 230 and of relay 222 so that relay 221 was connected in the supervisory circuit previously traced to maintain relays 221 and 223 energized, but upon the permanent energization of relay 222 due to the answering of the called subscriber, the super Visory circuit is permanently opened at the outer armature and make-before-break contact of relay 222 and no circuit will be completed for supervisory relay 223. When,

therefore, relay 203 is deenergized, after a short interval, relay 207 will be de'e'nergized to interrupt the circuits of relays 217 and 211 so that no groundwill now be connected to conductor 238 to maintain relays 213 and 214 energized and these relays will retract their armatures. Relay 214 in retracting its armature completes a circuit from ground, armature and back contact of relay 223 back contact of relay 214, front contact and righthand armature of relay 209, back contact and outer right-hand armature of relay 212,

gization otrelay L8 and ooniluc A :8, a circuit Wlll be completed from ounded battery, through the lei 'ftl relay 4'30. brush c conductor contact and left-hand armature r lay conductor 1), through the WHMLBQ' rel 49 to ground. Relays 49 and so a" ergized in this circuit, relay 50 sto selector switch G and starting the sent distributer S in the sam manner in wl hrelay 5O started the operation of S when signals were transmited i X to office Y. Relay as completes a from ground, armature and this relay through the wind of relay armature and back contact of relay 5.2, innr left-hand armature and upper contact lay 50 to grounded battery to ener lay 71'. Relay 7 1 in attracting its leitarn'iature completes a locking circuit for itself independent relay 49 and tracting its right-hand armature disconn The distributer S and receivin tributer R at otlice EL now operate in the same manner previously described to send a code signal consisting of six current i pulses of which the first, third and of negative polarity. In response to :7 nail locking relays 2'5 29 and 32 at are energized and lock a up so that when brush 18 reaches segments 23 and 25 of dis tributer R an impulse of current of positi polarity will be transmitted from the po-' tive pole of gounded batter and lower armature or relay over the circuit previously traced o ductor E 18 through the right-hon ing of relay 62 to ground. membered that the transmission or if I flux of such a direction as to aid that cause by the current flowing through t e left-hand locking winding of this relay to cause the energization of this relay. llow, howeven a: impulse of current of positive polarity is receiver. over conductor E 18 anl transmitted through the righthangl winding of This current causes a magnetic {1* x. amount and opposite in directio caused by the current flowing A locking winding of relay 6;, to this relay so that relay 62 is rendered inert. In retracting its left-hand armature relav 62 again completes the previously traced oi? that I inc cuit for slow release relay 63 while in retract ing its right-hand armature, relay 62 intorru ats the shunt circuit through resistance 69 and the Winding of marginal relay 53 to decrease the current flowing through marginal relay 53 to a point at which this relay retracts its armatui" to extinguish supervisory lamp The operator at offic X is thereby informed that the called subscriber has answered the call and that the conversation is now in progress. will be remembered that upon the engagement by brush 8" of sending distributer S, with segment 1%, a circuit was completed for relay 51, which in turn completed a circuit from grounded battery, inner left-hand armature and front contact of relay 50 baclr contact and arinm ture of relay 52, armature and front contact of relay 51. brush 7; conductor B 18' through the winding of relay 208 to ground. Relay 208 was energized in this circuit and in attracting its left-hand armatures, interrupted the locking circuit previously traced for relays 20 i and to deenergize 1%) these relays. Upon th by brush 9 0r segment 15 of distributor S a circuit was completed for relay 52' which in at tracting its armature opened the oi; cuit just traced for relay 208 to deenergize this relay. It is, therefore, apparent that during the couvers tion. :elays 5590 and 216 will be maintained energized and that all other reindividual to tell line L 18 and located is? i OlLiCG f Wlll be inert.

K 7 4 I .2 memor /72c? to collect roost: replaces i the cozrrersaticn s 4 i M1 in pacin fl-1};

c ntact of slit-hand act of relay 204) erect or relay 9 d jack 220.

m and ri hthan d gized as the enand 2 ing equipment SE and to be received by receiving equipment RE. It will be remembered that the result of this signal was to send a negative impulse of current over conductor E 18 to cause the energiza-tion and locking up of relay 62, thereby completing a shunt circuit in parallel with that of re lay through the winding of marginal relay 53 to cause the lighting of th supervisory lamp (38. lays 200, 205, 209, 213, 214, 215, 21c and will be maintained in an energized condition at the conclusion of the transmission of the signal, all other relays individual to tell line L 18 at olfice Y being inert.

The operator at oyjicc X disconnects to cowl circuit F from toll Zine L 18.

The ope 'ator at ofiice X noticing the illumination of the supervisory lamp 68 is in formed that the conversation has been terininated and disconnects plug from jacli 66 thereby interrupting the circuits of relays 53 and 55. Relay 53 in deenergizing extinguisheg lamp 68. Relay 55 in opening its front contact, interrupts the locking circuit of relay 62 to deenergize this relay. In closing its back contact, relay 55 completes a circuit from ground, armature and back contact of relay 55, front contact and inner right-hand armature of relay 57, through the winding of relay 59, back contact and right-hand. armature of relay 60 to grounded battery. Relay 59 is energized in this circuit and locked up to ground at its ii most left-hand armature and front co under the control of relay 60. in att act its innermost lef -hand armature, ay 5 interrupts the locking circuits of relays 5 and 57 to deenergize these relays. in attracting its middle left-hand armature, re lay 59 connects ground to conductor C to cause the energization of start relay 41, while in attracting its outermost left-hand arnuiture, relay 59 connects conductor A to conductor D so that when brush G en conductor A 18, a circuit will be cornpleted from grounded battery, through the left-hand winding of relay 50, brush a, conductor A 18, back contact and outer lef hand armature of relay 6i, outermost lefthand armature and front contact of relay 59, conductor D, through the winding of relay 4-9 to ground. Relays 4-9 and 50 will be energized in this circuit and the sending equipment SE and receiving equipment will be operated in exactly the same manner as was described for the operation of sending equipment SE and receiving equ'pment BE, in response to the answering of the called subscriber at substation N. it will be remembered that the result of this operation was to send an impulse of current of positive polarity over the selected signaling receiving conductor E 18. Relay 200 is As in the previous case, re

exactly similar in its windings to relay 62 so that the receipt of this impulse of positive polarity over the similarly selected signaling receiving conductor E 18, will differentialize relay 209 and cause it to re ract its armature. In retracting its outer armature, relay 200 will interrupt the circuit of relays 223 and 221. iielay 221 in retracting its arniatiu'e will complete a circuit from grounded battery, through lamp 228, front conta and lower armature of relay 227, resistance 229, back contact and armature of relay 221 to ground, to liglt lamp 228. The operator at ollice Z noticing the lighted condition of lamp 228 is informed of the termination of the conversation and removes plug from jack 225 thereby causing the deenergization of relays 227 and 226.

Relay 200 in retracting its inner righthand armature completed a circuit from grounded battery, inner right-hand armature and back contact of relay 200, front contact and lower armature of relay 216 through thelamp 218 to ground, to light the lamp 218. in opening its inner front contact, relay 200 interrupted the circuits of relays 202, 205 and 209 to (la-energize these relays. Relay 223 in ale-energizing" opened the circuits of relays 218 and The operator at oflice Y observing the lighted condition of lamp 218 Withdraws plug 219 from jack 220 thereby interrupting the circuit of relay 215. Relay 215, in deenergizing opens the circuit of relay 216 to extinguish lamp 218 and all apparatus employed at offices X, Y and Z in completing the connection is now completely restored.

. l 'aFmcVbcP at substation N recalls opcmtor at ofice l.

subststion N,

. r by the of 18 and toll sw tchin trunk cirl 1 1 tr I nal the. operator, he may the oper r at oflice X by raoidly open] g and cl his switchboard or a:

v. n be remembered that after the answer of the called subscriber and thereafter dur ing tl c conversation, all the relays connected with the incoming end of toll line L 18 at oilice Y are controlled by signals received over the conductor ElS and the operation of the called line snpeiyisory relay 223 until relays 20 and 2:) energized. When the subs-riber, recalling the operator at otlice X, has opened his switchhook contacts by dejnessing the ewitchhoolz, the circuit for relay 231 is interr pted to deiinergiae this i .ay and vonseqi n T relay 222. Relay 222 in retracting its 5, atures'energises relay in the previously traced. circuit through the talking conductors of the toll switching trunk M and the incoming end of the line L 1.8 which circuit operates supervisory relay 223. When the recalling subscriber closes his switchhook contacts by releasing the switchhoolr, the circuit for relay 231 and consequently relay 222 is again completed. Relay 222 in retracting its armatures closes the holding circuit through the left-hand winding of relay 221 to maintain this relay energized but opens the circuit including supervisory relay 223 to delinergize this re lay. Thus relay 223 will be alternately energized and deenergized so long as the suh-- scriber at station N actuates his switchhook. Relay 214 is made slow to relea '2 so that it will remain energized during the intervals when the armature of supervisory relay 223 is retracted. Relay 210 is also made slow to release so as to hold its armature attracted during the intervals when relay 223 is energized. Relays 206 and 209 are also made slow to release to aid in sending the recall signal to oiiice X as will more fully appear hereinafter.

.Upon the energization of relay 223 in response to the depression of the switchhool: at substation N, the previously traced circuits for relays 48, 212, 213 and 214 are completed and these relays are ener ized and locked up in the same manner as was described in the case when the operator at oiiice Y inserted plug 219 into jack: 220 upon the first illumination of the guard lamp 218. It will be remembered that these operated to send a code signal consisting of sir; inipulses, namely which resulted in the transmission of an impulse of negative current over the conductor E 18 to ener 'hc-e signal receiving relay 62 at X. as in the former case, the energization of relay 62 completed the circuit to shunt relay thereby causing the operation of marginal relay 53 andv consequently illuminating lamp 63 before the operator. Relay '1 attractingv its left-hand armature inapted the L'ircuit of slow release relay so that a subsequent impulse of current recei ed over conductor E 13 will find lel'path to ground through g tile of signal. receiving relay 04 as well as through the right-hand winning of lay 62.

lluring the operation of the sending uipment SE in transmitting the signal just destribed, it will be remembered tl at lay was energized to interrupt the cirruits of elays 4-3 and 212 to dei ne these relays. opens, at

.. er left-hand armat the w dirl and 2 39 trout oi. v

r armature and front contact clay through the winding of relay 209, the baclz contart ant. inner .ghthand armature of relay 204 to ground, It will be remembered that the circuit for relay 208 is interrupted during the sending out of a signal so that after the signal has been sent only relays 200, 202, 205, 209, 213 and 214 will be in an energized condition.

In response to the first closing of the switclrhook contacts after their opening, relay 223 is deenergized opening its front contact which interrupts the previously traced locking circuit for relay 213. Relay 213 although somewhat slow in operating and releasing, is fast enough to denergize during the interval that the front contact of relay 223 remains open. In closing its back contact, relay 223 completes an energizing circuit for slow release relay 210 which may be traced from grounded battery, winding of relay 210, armature and front contact of relay 214, and back contact and armature of relay 223 to ground. Relay 210 in attracting its armature prevents the connection of ground to conductor 239 for as long as the recalling subscriber continues to actuate his switchhook. Before the opening of the front contact of relay 223 has had time to cause the closure of the normal contacts of relay 214 which would have applied ground to conductor 239, the subscriber again opens his switchhook contacts to energize relay 223. Relay 223 in energizing again completes the circuit for relays 48, 212, 213 and 214. The energization of relays 212 and 48 again causes the sending equipment SE to send a signal resulting in the transmission of an impulse of current of negative polarity over signal receiving conductor E 18 at oflice X. This impulse is transmitted in parallel through the right-hand windings of relays 62 and 64. S nce relay 62 is already energized and locked up, no effect is produced on this relay. Relay 64, however, is energized and a locking circuit is completed from grounded battery, left-hand armature and front contact and winding of relay 64,

and front contact and armature of relay 55 to ground. Relay 64 in attracting its right-hand armature disconnects from the armature of relay 64, the steady ground which has caused the continuous illumination of lamp 68 and replaces this ground connection by an intermittent connection to ground through the interrupter 72. The

iz-so its illumination before it began to flash and therefore would not be in danger of mistaking the recall signal for the steady illumination of lamp 68 which would indicate to her the termination of the call.

C'Vhen relay 212 at ofiice Y was energized to cause the sending of the second signal, a circuit was completed for relay 206 which may be traced from grounded battery, inner armature and front contact of relay 200, through the winding of slow release relay 200, right-hand normal contact of said relay, front contact and left-hand armature of slow release relay 209, the front contact and inner left-hand armature of relay 212 to ground. Relay 208 in attracting its inner left hand armature, opens the original looking circuit of relay 213, which relay is energized at this time and completes a new locking circuit for relay 213 which relay owing to its slow releasing character remains energized. This locking circuit may be traced from grounded battery, winding, front contact and right-hand armature of relay 213, inner left-hand armat ire and front contact of relay 206, back contact and inner righthand armature of relay 204 to ground. When, therefore, the switchhook contact at substation N is next closed to cause the deenergization of the front contact of relay 228, the only effect produced is the continued operation of relay 210 over the circuit previously traced. Upon the next opening of the switchhook contacts at substation N and consequent energization of relay 228, the closure of the front contact of relay 223 will maintain slow release relay 214 energized but will not affect relay 212 since the circuit previously traced for this relay is interrupted at the left-hand armature of relay 213 which is now locked up under the control of relay 204. Thus, subsequent actuation of the switchhook at substation l-l maintains slow release relays 210 and 214 energized but is without effect on the sending equipment SE so that no furthensignals are transmitted over the path P to office X and lamp 68 continues to flash before the operator notifying her of the recall. From the foregoing description it will be apparent that in recalling the operator at office X, the subscriber at substation N opens and closes his switchhook contacts in amore or less irregular manner causing the sending of only two code signals over the path P which result in the flashing of the lamp 68 at a steady rate to notify the operator that her attention is desired.

If, after repeatedly opening and closing his switchhook contacts to recall the operator at office X, the subscriber at station N should retain his receiver off its switchhook thereby causing the continued closure of the contacts, supervisory relay 223 would remain de'energized. After a short interval relay 214 would retract its armature thereby completing a circuit from grouno, armature and back contact of lay 228, normal contacts of relay 214, front contact and righthand armature of relay 209, back contact and outer right-hand armature of relay 212, through the winding of relay 204, back contacts and left-hand armatures of relay 208, conduct =11, through the winding of relay to 1 ounded battery. Relays 4S and 204 are e gizcd in this circuit and locked up throt n the front contact and inner right- 'niature of relay 204. Relay 204 in A g its inner right-hand back contact interrupts the previously traced locking circuits for relays 200 and 21.3 to deenergize these relays In attracting its left-hand armature, relay 204 connects conductor A18 to conductor so that upon the stopping J of the selector switch G with its brush a resting upon the contact individual to conductor $118, the previously traced circuit for relays 49 and 530 will be completed. l elay 49 will cause the energization of re- 71 in the manner previously described so that the signal sent out by distributer S will consist of six impulses of current of the following polarities: the receipt of this signal at oiiice X will cause the tra remission of an impulse of current of positive polarity over receiving conductor E 18. This positive impulse passing through the right-handwindings of relays 62 and 64 to ground will cause a magnetic flat; of opposite direction and equal amount to that caused by the current flowing through the left-hand locking windings of these relays and will thereby cause the differentialization and retraction of the armatures of relays 62 and 64. Relay 62in retracting its right-hand armature interrupts ti he shunt circuit about relay which had previously caused the intermittent operation of marginal relay to renderthis relay inert. Relay in retracting its armature extinguishes lamp 08 so that the operator at oifice X is now notified that the call is still in progress.

It will. be remembered that during the transmission of the signal which caused the cessation. of the flashing of lamp 68, relay 208 at oflice Y was energized in response to the energization of relay 51. Relay 208 in energizing interrupts, at its left-hand armatures, the circuit of relays 48 and 204; Relay 214 in retracting its armatures opens the circuit of relay 210 to deenergize this relay so that only relays 200 and 202 of the relays under the control of the supervisory relay 223 and signal receiving conductor E'lS are now energized and the condition at office Y is the same as before the recalling of the operator at oflice X.

If. after repeatedly opening and closing the switchhoolr contacts to recall the operator at office X, the subscriber at station N should leave the switchook contacts permanently open as by replacing his receiver on its switchhook, the supervisory relay 223 would remain energized. After a short interval, the continued opening of the back contact of relay 223 would cause the deenergization of slow release relay 210. Relay 210 in retracting its armature, completes a circuit which may be traced from ground, armature and back contact of relay 210, outer left-hand armature and front contact of relay 206, front contact and right-hand armature of relay 209, back contact and outer right-hand armature of relay 212 through the winding of relay 204, back contacts and left-hand armatures of relay 208, conductor G, through the winding of relay 48 to grounded battery. Relays 48' and 204 are energized in this circuit. Relay 48 starts the selector switch G to seek its ter minals individual to line L 18, and relay 204 in closing its inner right-hand front contact completes an obvious locking circuit for relays 48 and 204. Relay 204 in opening its inner right-hand back contact interrupts the previously traced locking circuits for relays 205, 209, 206 and 213 to deenergize these relays. In attracting its left-hand armature, relay 204 connects conductors A 18 and D so that in the manner previously described, relays 49 and 71 will be energized when brush a, of selector switch G comes to rest on the terminal of conductor A 18. The energization of common relay 71 will cause the signal sent over the conductor P in response to the energization of relay 48 to consist of siX impulses of current of the following polarities: This signal will, in the manner previously described, cause an impulse of current of positive polarity to be transferred over conductor E 18 at ofiice X, through the right-hand windings of relays 62 and 64 to ground, thereby differentializing those relays and extinguishing lamp As in the previous cases, relay 208 will be energized during the transmission of the signal to interrupt the circuit for relays 48' and 204 so that upon the deenergization of relay 208, in response to the attraction of the armature of relay 52", only relays 200, 202, 214 and 223 of the relays individual to line L 18 at its incoming end and under the control of supervisory relay 223 and signaling conductor E418 will be in an energized condition. Although relay 223 has been maintained energized throughout the cycle of operations just described, the energizing circuit for relay 213 was held interrupted at the outer right-hand armature of relay 204 while this armature was attracted and thereafter at the right-hand armature of relay 208 so that upon the deen er ization of relay 204 and thereafter of relay 208, the original traced energizing circuits for relays 48, 212 and 213, will be completed and a second signal will be transmitted over conductor P. Since, however, there is now no circuit completed for relay 204 and consequently none'for relays 49 or 71, the sixth impulse of the code signal which controls the polarity of current to be transmitted over the selected signal receiving conductor will be of positive polarity and thereby causing the transmission of an impulse of negative polarity over conductor E 18 at office X. It will be remembered that upon the deenergization of relay 62 in response to the signal transmitted, just previously to this one, relay 63 was energized to interrupt the signaling circuit through the right-hand winding of relay 64 so that no impulse of negative current will pass through the winding of relay 62 to energize this relay. Relay 62 in attracting its righthand armature again completes a circuit from ground, back contact and right-hand armature of relay 64, right-hand armature and front contact of relay 62, resistance 69, sleeve contacts of jack 66 and plug 65, through the winding of marginal relay 53 to grounded battery, thereby allowing suflicient current to flow through the winding of relay 53 to operate this relay and maintain lamp 68 steadily illuminated. The steady illumination of lamp 68 is an indication to the operator at ofiice X that the call has been terminated by the replacement of the receiver at station N on its switch hook. As in the case described when the operator at oilice Y inserted plug 219 into jack 220, the transmission of the signal which lighted the lamp 68 at office X re sulted in the energization of relay 208 to deenergize relays 48 and 212 thereby leaving relays 200, 202, 205, 209, 213 and 214 energized.

The operator at office X upon noting the termination of the call removes plug 65 from jack 66, thereby causing the sequence of operations previously described in connection with the breaking down, which results in the sending of an impulse of positive polarity over signal receiving conductor E 18 to differentialize relay 200. Relay 200 in opening its inner front contact, interrupts the circuits of relays 202, 205 and 209, and in opening its outer right-hand contact interrupts the circuits of relays 223 and 221 in the manner previously described. Relay 223 in deenergizing interrupts the circuits of relays 213 and 214 and relay 214 after an interval, opens its front contact to deenergize relay 210 so that all the relays associated with the incoming end of the line L 18 are now in normal condition. The operators at oflice Y and oiiice Z are notified of the termination of the connection in the manner previously described and remove plugs 219 and 22 1 from their respective jacks 220 and 225, whereupon all the apparatus employed in building up the connection is restored to normal condition. Use of busy baa/c jacks at ofices 1 and Z. At the time when the operator at oli'ice X in inserting the plug of cord circuit in the jack of the designated toll line L 18 caused the illumination of guard lamp 218 before the operator at oflice Y, it will be remembered that only relays 2G0 and 202 of those associated with the incoming end of toll line L 18 were energized. 1f the operator at oflice Y had, in the meanwhile, determined over the order wire circuit (not shown) that there were no idle trunks leading to otlice Z, she would, upon the illumination of lamp 218 have inserted plus 219 into the busy back jack 235. Relays 210 and 216 would have thereupon been energized over olwious circuits, and relay 223 would be intermittently energized and deenergized in exactly the same manner as was described in connection with the recalling of the operator at oflice X by the subscriber at station N. The first energization of relay 223 would have sent out a signal to cause the steady illumination of lamp 68 before the operator at office X, but before this operator could have interpreted this signal as a ringing signal, relay 223 would have been de zinergized to send a second signal of exactly the same character as was described in connection with the recalling of the operator at o'liice X which would have resulted in the energization of relay 6 1 to cause the intermittent operation of lamp 68. The flashing of lamp 68 following next in succession to the insertion of the plug of her cord circuit in the jack of the designated toll line is an indication to the operator at oilice X that she will be unable to complete the desired connection on account of the busy condition of either a link in the circuit or in the called line and she may so iniorm the calling subscriber, thereupon removing the plug of the cord circuit from its'associated ac]: to cause the sending of a signal to office Y which will light lamp 218 to notify the operator at ofiice Y that the connection has been abandoned.

In case the operator at oflice Z, after assigning toll switching trunk circuit for use in connection with office Y to office Z, should find the "called line busy, she would insert plug 22 1 in busy back jack 236 before her position, thereby causing the operation of relays 226 and 227. Relay 227 in attracting its upper armature completes an obvious circuit to cause the intermittent operation of relay 281. Relay 231 in intermittently closing and opening its front contact would intermittently energize and deenergize relay 222 so as to alternately exclude and include the windings of relay 221 in the end of toll switching trunk circuit M leading to the tip and ring contacts of jack 220. Thus, when the operator at oiiice Y inserts plug 219 into jack 220 upon the illumination of guard lamp 218, relay 228 will be intermittently energized and deenergized in the circui including relay 221 and the two signals previously described will be transmitted to ofhce X to cause the flashing of lamp 68 before the operator. As in the case when the operator oflice Y employed busy back jack 285, the operator at oliice X is thereby notilied of the busy condition of some part of the circuit desired for completing the connection and may thereupon abandon the call.

The operation described above with reference to building up a connection over the trunk line L 18 through toll switching trunk circ M to station N and the breaking ut down of such a connection is typical of that taking place in building up and breaking down connection over any one of the trunk ii i to which the signaling path P is commen The only essential difference in opera 11, so far as the establishment of a connection over the di'rerent toll lines is concerned, it that different code signals are employed for the different trunk lines and while this invention is not limiter, to any particular arrangement of code signals, the codes shown in the following tables have been found to be very satisfactory for a total of thirty lines served by the same common signaling path.

Signals from oflicc X to office Y. slgnals 2322, gt Y to Re- T nk (1 Dis- Recelveii Flashline No. Guard connect. g g a ofi hook. ing.

1 3 3 36 3 36 3 2 4 4 46 4 16 4 3 5 5 56 5 56 5 1 31 3% 346 34 346 34 5 35 35 358 35 356 35 6 45 45 456 45 456 45 7 315 345 3155 345 3156 315 S 2 2 2G 2 26 2 9 23 23 236 23 236 23 10 21 21 216 24 216 21 11 25 25 256 25 255 25 12 234 234 2315 234 2346 231 13 235 235 2356 235 2358 235 11 245 245 2156 245 2456 245 15 2315 2345 23456 2345 23456 2315 12 1 1 16 1 1G 1 1 12 12 126 12 126 12 18 13 13 135 13 136 13 1Q 14 14 14$ 14 146 11 20 15 15 155 15 15G 15 21 123 123 1236 23 1236 123 22 121 124 1246 121 1216 124 3 125 125 1256 125 1256 125 21 134 131 1346 131 1346 131 o 135 135 1353 135 1355 3 22 145 145 1156 145 1156 27 1231 1234 12315 1215 12346 1 r 28 1235 1235 12356 1235 12350 1 5 29 1245 1245 12456 1245 12456 1215 30 1345 1315 13156 1345 13456 1315 in this table, the numbers in the first column indicate the numbers assigned to the trunk lines, while the numbers in the remaining columns indicate the order of the impulses of each group of six. The numbers 1, 3 appearing in the first, second, fourth, and sixth columns of the horizontal row associated with trunk line 18 indicate that the first and third impulses 01" the code signal transmitted in response to the guard, ring, receiver on hook, and flashing signals will be negative, while the numbers 1, 3, 6 appearing in the third and fifth columns opposite line 18 indicate that the first, third and sixth impulses of the code signals transmitted are negative. The various code signals represented in the table are determined by the polarities of current connected with the contacts of the levels one to five oi the automatic selector switches G and G, and by the energized or inert condition of relays 71 and 71 during signaling.

W hat is claimed is:

1. in a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the diiierent trunk lines, each code signal comprising a plurality of current impulses, means common to the trunk lines for determining the character of certain of the impulses of each code signal, additional independent means common to the trunk lines for determining the character of other of the impulses of each code signal, and means individual to each trunk line for controlling the operation of said additional means.

2. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the diilerent trunk lines, each code signal comprising a plurality oi current impulses, a normally inactive switching device common to the trunk lines for determining the character of some of the impulses or" each code signal, a relay common to the vice common to the trunk lines for determining the character of some of the impulses of each code signal, a relay common to the trunk lines for determining the character of other of the impulses of each code signal, means individual. to each trunk line responsive to certain changes in condition of said trunk line for associating said switching device with said trulr line, and a relay indi vidual to each trunk line responsive to other changes in condition of said trunk line for associating said switching device with said trunk line and causing the operation or" said impulse character determining relay.

4. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the diiierent trunk lines, each code signal comprising a plurality of current impulses, a normally inactive switching device common to the trunk lines for determining the character of certain of the impulses or" each code signal, means for operating said switching device in response to any change in condition of any trunk line, a relay common to the trunk lines for determining the character of another impulse of each code signal, and means individual to each trunk line operated in response to certain changes of condition of its associated trunk line for operating said relay.

5. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, a signaling device at one station, means the other station for transmitting over the signaling path code signals individual to the different trunk lines, each code signal comprising a plurality 01 current imother of the impulses of each code signal,

means at said other station responsive to two rapid changes in the condition of one of said trunk lines to successively actuate said switching device twice to send two code signals over said signaling path to cause the intermittent operation of said signaling de vice, said switching device being unafiected by additional rapid changes, and means responsive to the cessation of such rapid changes to actuate said switching device and said common relay to send a single code signal of different character over said signaling path to render said signaling device inert. ln witness whereof, ll hereunto subscribe my name this 17th day of July A. 1)., 1920.

HUGH D. MAQPHERSON. 

